Airfoil with body and cover panel

ABSTRACT

An airfoil includes a body that has rib nodes that each define a node cavity therein. A cover panel is carried on the body over the rib nodes. The cover panel includes tabs that project into the node cavities. Plugs are disposed in the node cavities and pinch the tabs against the node cavities to lock the cover panel on the body.

BACKGROUND

Airfoils, and particularly fan blades, may be made from multiple piecesin order to reduce weight and ease manufacturing. As an example, ahollow blade may be formed by securing two airfoil shell pieces togetherto provide an aerodynamic blade shape. An adhesive is used to bond thepieces together. A challenge, however, is that a relatively large amountof surface area is needed to strongly bond the pieces together andprovide structural strength to the airfoil. This results in the use ofthick interfacial ribs that add weight, thereby undermining the ultimategoal.

SUMMARY

An airfoil according to an example of the present disclosure includes abody that has rib nodes that define a node cavity therein, and a coverpanel carried on the body over the rib nodes. The cover panel has tabsthat project into the node cavities. Plugs are disposed in the nodecavities and pinch the tabs against the node cavities, locking the coverpanel on the body.

In a further embodiment of any of the foregoing embodiments, each of theplugs includes an exposed surface that is flush with the cover panel.

In a further embodiment of any of the foregoing embodiments, each of therib nodes includes an undercut.

In a further embodiment of any of the foregoing embodiments, the coverpanel includes a plurality of the tabs in each of the node cavities.

In a further embodiment of any of the foregoing embodiments, the tabsare flaps bent from the cover panel.

In a further embodiment of any of the foregoing embodiments, the coverpanel is a fiber-reinforced polymer composite, and the body is metal.

In a further embodiment of any of the foregoing embodiments, each of thenode cavities is symmetric.

In a further embodiment of any of the foregoing embodiments, each of thenode cavities is round.

In a further embodiment of any of the foregoing embodiments, the plugsare polymer-based.

In a further embodiment of any of the foregoing embodiments, the plugsare fiber-reinforced polymer composite.

In a further embodiment of any of the foregoing embodiments, each of theplugs includes an exposed surface that is flush with the cover panel.Each of the rib nodes includes an undercut. The cover panel includes aplurality of the tabs in each of the node cavities, and the tabs arefolds bent from the cover panel.

An airfoil according to an example of the present disclosure includes ametal body, a cover panel carried on the metal body, and push fastenersthat extend through the cover panel and lock the cover panel on themetal body.

In a further embodiment of any of the foregoing embodiments, each of thepush fasteners includes flexible barbs.

In a further embodiment of any of the foregoing embodiments, each of thepush fasteners includes a head that is embedded in the cover panel.

In a further embodiment of any of the foregoing embodiments, the coverpanel includes stitching adjacent the head of the push fasteners.

In a further embodiment of any of the foregoing embodiments, the metalbody includes holes receiving the push fasteners, and the holes includeundercuts.

In a further embodiment of any of the foregoing embodiments, the metalbody includes straight holes receiving the push fasteners.

A gas turbine engine according to an example of the present disclosureincludes a fan, a compressor section, a combustor in fluid communicationwith the compressor section, and a turbine section in fluidcommunication with the combustor. The fan has airfoils according to anyof the foregoing examples.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the present disclosure willbecome apparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

FIG. 1 illustrates a gas turbine engine.

FIG. 2 illustrates an example airfoil of the gas turbine engine.

FIG. 3 illustrates a magnified view of a portion of the airfoil of FIG.2.

FIG. 4 illustrates a sectioned view of a representative portion of theairfoil.

FIG. 5 illustrates a top-down view of a representative portion of theairfoil.

FIG. 6 illustrates a view of flaps cut into an uncured cover panel.

FIG. 7 illustrates an airfoil with a push fastener.

FIG. 8 illustrates a rib that includes a flange and an adhesive layer.

FIG. 9 illustrates an airfoil with a push fastener and stitching.

FIG. 10 illustrates an airfoil with a push fastener and straight hole.

FIG. 11 A illustrates a node that defines a node recess, a cover panelthat conforms to the node recess, and a fastener that has a head thatsits in the node recess.

FIG. 11B is a sectioned view of FIG. 11A.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. The fan section 22 drivesair along a bypass flow path B in a bypass duct defined within a nacelle15, and also drives air along a core flow path C for compression andcommunication into the combustor section 26 then expansion through theturbine section 28. Although depicted as a two-spool turbofan gasturbine engine in the disclosed non-limiting embodiment, it should beunderstood that the concepts described herein are not limited to usewith two-spool turbofans as the teachings may be applied to other typesof turbine engines including three-spool architectures.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis A relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided, and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects, a first (or low) pressure compressor 44 and a first (orlow) pressure turbine 46. The inner shaft 40 is connected to the fan 42through a speed change mechanism, which in exemplary gas turbine engine20 is illustrated as a geared architecture 48 to drive a fan 42 at alower speed than the low speed spool 30. The high speed spool 32includes an outer shaft 50 that interconnects a second (or high)pressure compressor 52 and a second (or high) pressure turbine 54. Acombustor 56 is arranged in exemplary gas turbine 20 between the highpressure compressor 52 and the high pressure turbine 54. A mid-turbineframe 57 of the engine static structure 36 may be arranged generallybetween the high pressure turbine 54 and the low pressure turbine 46.The mid-turbine frame 57 further supports bearing systems 38 in theturbine section 28. The inner shaft 40 and the outer shaft 50 areconcentric and rotate via bearing systems 38 about the engine centrallongitudinal axis A which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path C. The turbines 46, 54 rotationally drivethe respective low speed spool 30 and high speed spool 32 in response tothe expansion. It will be appreciated that each of the positions of thefan section 22, compressor section 24, combustor section 26, turbinesection 28, and fan drive gear system 48 may be varied. For example,gear system 48 may be located aft of the low pressure compressor, or aftof the combustor section 26 or even aft of turbine section 28, and fan42 may be positioned forward or aft of the location of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five 5:1. Low pressure turbine 46 pressure ratio is pressuremeasured prior to inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1 and less than about 5:1. Itshould be understood, however, that the above parameters are onlyexemplary of one embodiment of a geared architecture engine and that thepresent invention is applicable to other gas turbine engines includingdirect drive turbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet (10,668 meters). The flight condition of 0.8 Mach and35,000 ft (10,668 meters), with the engine at its best fuelconsumption—also known as “bucket cruise Thrust Specific FuelConsumption (′TSFC)”—is the industry standard parameter of lbm of fuelbeing burned divided by lbf of thrust the engine produces at thatminimum point. “Low fan pressure ratio” is the pressure ratio across thefan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The lowfan pressure ratio as disclosed herein according to one non-limitingembodiment is less than about 1.45. “Low corrected fan tip speed” is theactual fan tip speed in ft/sec divided by an industry standardtemperature correction of [(Tram ° R)/(518.7° R)]{circumflex over( )}0.5. The “Low corrected fan tip speed” as disclosed herein accordingto one non-limiting embodiment is less than about 1150 ft/second (350.5meters/second).

FIG. 2 illustrates an airfoil 58, which in this example is a rotatableblade of the fan 42 (see FIG. 1) of engine 20. It is to be appreciatedthat, although examples herein may be described with reference to a fanblade, this disclosure may also be applicable to static fan vanes oreven other types of blades, vanes, or airfoils. As will be appreciatedfrom the description that follows, the airfoil 58 utilizes an attachmentscheme that provides strong securement of the various pieces, as well asfacilitating weight-reduction and structural integrity.

The airfoil 58 generally has two pieces, including a body 60 and a coverpanel 62, although the body 60, the cover panel 62, or both couldalternatively be provided in multiple sub-pieces. As shown, the coverpanel 62 is separated from the body 60 to reveal the configuration ofthe body 60; however, dashed lines are used to indicate the final,attached position of the cover panel 62 on the body 60. Together, thebody 60 and the cover panel 62 delimit an airfoil profile that includesa leading edge 64, a trailing edge 66, a pressure side 68, and a suctionside 70. In this example, the airfoil 58 also includes a root 72, whichhas a dovetail shape for securing the airfoil 58 in a doveslot of arotor hub. In this example, the body 60 defines the leading and trailingedges 64/66, the pressure side 68, and the root 72. The cover panel 62thereby provides the suction side 70 of the airfoil 58.

The airfoil 58 is a hybrid of different materials. For example, the body60 is formed wholly or primarily of a metal alloy, such as a titaniumalloy, and the cover panel 62 is formed of a polymer-based composite,such as a fiber-reinforced polymer matrix composite. The metal alloy ofthe body 60 provides good strength and wear/erosion resistance, whilethe polymer-based composite serves to reduce weight.

The fiber-reinforced polymer matrix composite is not particularlylimited but may include one or more layers of fibers disposed in apolymer matrix, for example. Example fibers may include carbon or glassfibers, and example polymers may include thermoset or thermoplasticpolymers. In one example, the polymer is epoxy. The fibers may becontinuous or discontinuous. If continuous, the fibers may be providedas a unidirectional tape, two-dimensional woven fabric,three-dimensional woven fabric, biaxial or triaxial braided fabric, orother fiber configuration. The cover panel 62 may also include a singlelayer of fiber-reinforced polymer matrix composite or multiple layers,which may be the same or different with regard to the any or all of thefiber architecture, fiber composition, polymer composition, andvolumetric amounts of fibers and polymer.

Referring to the magnified view of the body 60 in FIG. 3, opposite thepressure side 68 the body 60 includes a recess 74 over which the coverpanel 62 is attached, such that the airfoil 58 is at least partiallyhollow. The recess 74 is setback and flanked by exterior aerodynamicsurfaces 75. The recess 74 may define a perimeter ledge 74 a upon whichthe cover panel 62 sits. The cover panel 62, in its final installedposition, is flush with the surfaces 75. The body includes ribs 76 inthe recess 74. In this example, the ribs 76 extend primarilylongitudinally with respect to inner and outer ends of the airfoil 58.The ribs 76 serve to provide structural reinforcement to the airfoil 58(particularly in the longitudinal pull-direction of the airfoil 58), aswell as support the cover panel 62.

The ribs 76 intersect at rib nodes 78. In this example, the rib nodes 78are configured in an array of longitudinal rows. Each rib node 78 isformed of a rib wall 78 a that defines or circumscribes a node cavity80. In this example, the rib walls 78 a, and thus the node cavities 80,are round. As will be appreciated, the rib walls 78 a and node cavities80 could alternatively be oval or other enclosed shape. Most typically,however, for reasons that will become apparent below, the node walls 78a and node cavities 80 have a shape that is free of sharp or distinctcorners. If the ribs 76 are not needed for reinforcement, some or all ofthe ribs 76 may be excluded, leaving the nodes 78 as free-standingstructures formed of the rib walls 78 a.

FIG. 4 illustrates a sectioned view through a representative portion ofthe airfoil 58, and FIG. 5 illustrates a top-down view of arepresentative portion of the airfoil 58. The cover panel 62 includestabs 62 a that project into the node cavity 80. A plug 82 is disposed inthe node cavity 80. The plug 82 pinches the tabs 62 a against the ribwalls 78 a of the node cavity 80, thereby locking the cover panel 62 onthe body 60. In this regard, the relatively continuous and smoothprofile of the node cavity 80 facilitates good contact and pressuredistribution between the plug 82 and the tabs 62 a.

To further facilitate mechanical locking, the rib wall 78 a that formsthe rib node 78 may include an undercut 78 b. The plug 82 may pinch thetabs 62 a into the undercut 78 b and thereby partially wrap the tabs 62a around the rib wall 78 a to prevent the tabs 62 a from easily liftingout of the node cavity 80.

As an example, as shown in an isolated view in FIG. 6, the tabs 62 a maybe flaps that are cut from the cover panel 62. For instance, prior tofully curing the cover panel 62 during fabrication, the cover panel 62may be cut in a cross pattern to form the flaps. The flaps may then bebent out-of-plane from the remainder of the cover panel 62 so that theflaps can extend into the node cavity 80. As will be appreciated, otherpatterns could be used to produce other flap shapes.

The flaps may additionally be trimmed, to reduce the number of flapsand/or reduce size and weight. However, the flaps should at least be ofa size that provides ample area for contact with the plug 82. Forinstance, in the example shown in FIG. 4, the tabs 62 a extend down thesides of the rib walls 78 a and partially across the bottom of the ribcavity 80. Alternatively, the tabs 62 a may be trimmed so as to extendonly down to the bottom, or just short of the bottom, of the rib cavity80. Should the tabs 62 a be too small, for example as to extend onlyless than 50% the distance down the rib walls 78 a to the bottom, thearea for contact with the plug 82 may be insufficient to effectivelypinch and secure the tabs 62 a.

The bending of the flaps may be conducted prior to positioning the coverpanel 62 on the body 60 or after such positioning. Once positioned, withthe tabs 62 a in the node cavity 80, the plug 82 is inserted into thenode cavity 80. As an example, the plug 82 is initially a liquid orformable semi-solid that is introduced, such as by injection orpressing, into the node cavity 80. The liquid or formable semi-solidsubsequently solidifies to form the final plug 82. The plug 82 traps thetabs 62 a against the rib walls 78 a, to thereby fasten the cover panel62 to the body 60.

As will be appreciated, the plug 82 has an exposed (aerodynamic) surface82 a (FIG. 4) on the exterior of the airfoil 58. The exposed surface 82a is flush with the cover panel 62 so as to form a relatively smooth andcontinuous aerodynamic surface. If, after fabrication, the plug 82 isnot flush, the plug 82 may be machined, sanded, or otherwise smoothed sothat it is flush.

The material of the plug 82 may be co-processed with the cover panel 62.For example, the plug 82 and the cover panel 62 may be formed from thesame composition of material or at least a common base polymer such thatcuring steps can overlap or be conducted simultaneously. In this regard,the plug 82 and the cover panel 62 may, in one example, be formed ofepoxy or other thermoset polymer. Most typically, the selected polymerwill be of relatively high strength and rigidity, rather than anelastomeric. Use of the same composition of material or at least of acommon base polymer may also enhance adhesion bonding between the plug82 and the cover panel 62, thereby facilitating locking the plug 82 inplace. Alternatively, the plug 82 may be formed of a differentcomposition than the cover panel 62 or at least a different basepolymer. For instance, the plug 82 may be formed of a thermoplasticbase-polymer that can be melted and injected into the node cavity 80.

The material of the plug 82 may also contain reinforcement or fillers inorder to modify the properties for enhanced pinching of the tabs 62 a.As an example, the material of the plug 82 may contain chopped fibers,such as short glass fibers, to increase strength and rigidity tofacilitate trapping the tabs 62 a.

The cover panel 62 may be fully or partially pre-fabricated prior toinstallation on the body 60 or partially or fully formed in place on thebody 60. Pre-fabrication may include fully or partially curing the coverpanel 62 and plug 82 prior to installation on the body 60, or fully orpartially forming the cover panel 62 and plug 82 if formed ofthermoplastic. If the cover panel 62 is formed from thermoplastic, itcan be heated and re-shaped locally to conform to the body 62 and ribnodes 78. Local thermal forming is not possible if the cover panel 62 isformed from thermoset and is fully cured. If the cover panel 62 iscured/consolidated in situ on the body 60 during assembly, rigid orsemi-rigid members may be provided in the recess 74 to support the coverpanel 62 prior to and during the curing. One example of such membersinclude foam inserts.

FIG. 7 illustrates a representative portion of another example airfoil158 that also includes a body 160 and a cover panel 162. In thisdisclosure, like reference numerals designate like elements whereappropriate and reference numerals with the addition of one-hundred ormultiples thereof designate modified elements that are understood toincorporate the same features and benefits of the correspondingelements. The body 160 and cover panel 162 may generally have the sameshape as shown in FIG. 1. However, rather than the rib nodes 78 and plug82, the airfoil 158 employs push fasteners 184 (one shown). The pushfasteners 184 may be used in the locations where the rib nodes 78 areshown in FIG. 1. The push fasteners 184 extend through the cover panel162 and lock the cover panel 162 on the body 160.

In this regard, the body 160 is configured with holes 186 that receiveand lock the push fasteners 184. For instance, the holes 186 may definedin ribs of the body 160. As an example, the holes 186 me be used in thesame or similar locations as the nodes 78 of the prior examples. In theexample illustrated in FIG. 7, the push fastener 184 is configured as acantilever snap-fit with one or more flexible barbs 184 a that extendfrom a head 184 b. Upon insertion into the hole 186, the barbs 184 ainitially compress inwards to fit through the narrow portion of the hole186. The hole includes an undercut 186 a, and upon reaching the undercut186 a during insertion the barbs 184 a decompress and release outwards.The release cause the barbs 184 a to engage the upper edge of theundercut, thereby preventing the snap-fit fastener 184 from retractingfrom the hole 186. The head 184 b is engaged with the cover panel 162and thereby fastens the cover panel 162 to the body 160.

In this example, the head 184 b is embedded in the cover panel 162. Forinstance, the cover panel 162 is formed of multiple layers, and the head184 b is buried among the layers. The head 184 b, therefore, is notexposed on the exterior surface of the cover panel 162. In a furtherexample, the multiple layers of the cover panel 162 include one or morefiber-reinforced layers, such as layers 188 a/188 b, and a surface filmlayer 188 c. For instance, the layers 188 a/188 b may be formed of thefiber-reinforced polymer composite described above. In one example, thefiber structure of one or both of the layers 188 a/188 b is selected toapproximate an isotropic material, to facilitate mechanical and thermalcompatibility with the body 160. For instance, the layers 188 a/188 beach include a 0/+60/−60 triaxial braid, which provides the cover panel162 with in-plane quasi-isotropic properties. In a further example, thefibers in the triaxial braid are glass fibers, which provides acoefficient of thermal expansion that closely matches the coefficient ofthermal expansion of a titanium body 60.

The surface film layer 188 c serves to enhance resistance towear/erosion. For instance, the surface film layer 188 c may be formedof an elastomer, such as a fluoroelastomer.

As also shown in FIG. 7, an adhesive layer 190 may optionally be usedbetween the cover panel 162 and the body 160. For instance, the adhesivelayer 190 may be provided on a perimeter ledge of the body 160, similarto the perimeter edge 74 a shown in FIG. 3. The adhesive layer 190 maybe, but is not limited to, epoxy. Although the push fasteners 184 securethe cover panel 162 on the body 160, the adhesive layer 190 may be usedto further facilitate securement and/or reduce play between the coverpanel 162 and the body 160.

In a further example shown in FIG. 8, the ribs 76 may include a flange76 a upon which the cover panel 162 sits. The adhesive layer 190 may besituated on the flange 76 a. The adhesive layer 190 on the flange 76 amay be used to increase the surface bonding area in addition to adhesiveon the perimeter ledge. The flange 76 a thereby provides additionalsurface area for the purpose of bonding, yet minimizes mass of the body162 in comparison to a solid body or thicker ribs.

FIG. 9 illustrates a further example in which the cover panel 162includes stitching 192 adjacent the head 184 b of the push fastener 184.The stitching reinforces the cover panel 162 and facilitates reductionin delamination between the layers 188 a/188 b, particularly during animpact. As an example, the stitching 192 may be formed of fibers ofaramid, carbon, glass, or polyethylene, but is not limited thereto.

FIG. 10 illustrates another example of a push fastener 284. In thisexample, the push fastener 284 includes radial flexible barbs 284 a andthe body 160 includes a straight hole 286. The barbs 284 a are carriedon a shank that extends from the head 284 b. The barbs 284 a is receivedinto the straight hole 286 to secure the cover panel 162 to the body160. Upon insertion of the barbs 284 a into the hole 286, the barbs 284a are compressed and deflect or deform. The barbs 284 a tend todecompress and thus press outwards on the hole 286 to hold the fastener284, and thus the cover panel 162, in place.

In a further example, the push fastener 184/284 may be installed “wet”with a paste adhesive to further bond and strengthen the attachment ofthe cover panel 162 to the body 160. In this regard, the push fasteners184/284 may include one or more internal channels, depicted at 286(FIGS. 7, 9, and 10) to permit injection of the adhesive paste throughthe head of the fasteners 184/284 and into the hole 186/286 to bond thefasteners 184/284 to the sides of the hole 186/286.

FIGS. 11A and 11B illustrate a modified example in which the node 78defines a node recess 78 c. In this example, the cover panel 162conforms to the node recess 78 c such that there is a dimple 162 b inthe cover panel 162. The head 284 b of the fastener 284 is situated inthe dimple 162 b. This “low profile” configuration permits the head 284b to sit flush with, or below, the surface of the cover panel 162immediately surrounding the dimple 162 b, to enhance aerodynamics.

Although a combination of features is shown in the illustrated examples,not all of them need to be combined to realize the benefits of variousembodiments of this disclosure. In other words, a system designedaccording to an embodiment of this disclosure will not necessarilyinclude all of the features shown in any one of the Figures or all ofthe portions schematically shown in the Figures. Moreover, selectedfeatures of one example embodiment may be combined with selectedfeatures of other example embodiments.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthis disclosure. The scope of legal protection given to this disclosurecan only be determined by studying the following claims.

What is claimed is:
 1. An airfoil comprising: a body having rib nodesthat define a node cavity therein; a cover panel carried on the bodyover the rib nodes, the cover panel including tabs that project into thenode cavities; and plugs disposed in the node cavities and pinching thetabs against the node cavities, locking the cover panel on the body. 2.The airfoil as recited in claim 1, wherein each of the plugs includes anexposed surface that is flush with the cover panel.
 3. The airfoil asrecited in claim 1, wherein each of the rib nodes includes an undercut.4. The airfoil as recited in claim 1, wherein the cover panel includes aplurality of the tabs in each of the node cavities.
 5. The airfoil asrecited in claim 1, wherein the tabs are flaps bent from the coverpanel.
 6. The airfoil as recited in claim 1, wherein the cover panel isa fiber-reinforced polymer composite, and the body is metal.
 7. Theairfoil as recited in claim 1, wherein each of the node cavities issymmetric.
 8. The airfoil as recited in claim 1, wherein each of thenode cavities is round.
 9. The airfoil as recited in claim 1, whereinthe plugs are polymer-based.
 10. The airfoil as recited in claim 1,wherein the plugs are fiber-reinforced polymer composite.
 11. Theairfoil as recited in claim 1, wherein each of the plugs includes anexposed surface that is flush with the cover panel, each of the ribnodes includes an undercut, the cover panel includes a plurality of thetabs in each of the node cavities, and the tabs are folds bent from thecover panel.
 12. An airfoil comprising: a metal body; a cover panelcarried on the metal body; and push fasteners extending through thecover panel and locking the cover panel on the metal body.
 13. Theairfoil as recited in claim 13, wherein each of the push fastenersincludes flexible barbs.
 14. The airfoil as recited in claim 13, whereineach of the push fasteners includes a head that is embedded in the coverpanel.
 15. The airfoil as recited in claim 14, wherein the cover panelincludes stitching adjacent the head of the push fasteners.
 16. Theairfoil as recited in claim 13, wherein the metal body includes holesreceiving the push fasteners, and the holes include undercuts.
 17. Theairfoil as recited in claim 13, wherein the metal body includes straightholes receiving the push fasteners.
 18. A gas turbine engine comprising:a fan; a compressor section; a combustor in fluid communication with thecompressor section; and a turbine section in fluid communication withthe combustor, the fan having airfoils that each include a body havingrib nodes that define a node cavity therein, a cover panel carried onthe body over the rib nodes, the cover panel including tabs that projectinto the node cavities, and plugs disposed in the node cavities andpinching the tabs against the node cavities, locking the cover panel onthe body
 19. The gas turbine engine as recited in claim 18, wherein eachof the plugs includes an exposed surface that is flush with the coverpanel, each of the rib nodes includes an undercut, the cover panelincludes a plurality of the tabs in each of the node cavities, and thetabs are folds bent from the cover panel.